The SFH618A-3 is a Vishay single-channel phototransistor optocoupler in a 4-DIP through-hole package. Its defining parametric is the current transfer ratio (CTR) bin: guaranteed minimum 100% and maximum 200% at a forward current of 1 mA. This 2:1 spread gives the designer a predictable drive range for the output transistor, which directly sets the load resistor value and the logic-level threshold on the receiving side. A CTR floor of 100% at only 1 mA input means the LED drive current can be kept low, saving power in isolated digital interfaces or PLC input modules.
Isolation voltage and temperature range
Rated for 5300 Vrms isolation, this part suits reinforced-insulation applications in industrial power supplies, motor drives, and medical equipment where galvanic isolation between control and high-voltage domains is mandatory. The 55 V output breakdown and 50 mA per-channel output current handle typical logic-level translation and low-power relay drive without extra buffering.
Switching speed and timing budget
It is a good fit for DC signal detection, status feedback, and low-frequency data transmission up to a few tens of kilohertz. For faster interfaces like SPI or CAN isolation, a digital isolator with CMOS output stages would be the correct choice.
Lifecycle and compliance
The through-hole 4-DIP package is straightforward to hand-solder or wave-solder, and the Tube shipping quantity suits both prototyping and medium-volume production runs.